1. Field of the Invention
This invention relates generally to plastic lenses and, more specifically, to a method of selectively identifying plastic lenses.
2. Description of the Prior Art
The method of marking ophthalmic lenses or lenses which must be visually clear has been accomplished in the art by various means. A typical prior art method is shown in the Drescher U.S. Pat. No. 1,475,473. Drescher marks a glass lens by altering the composition of the lens by subjecting the lens to "the action of rays emanating from the vacuum tube through which a current of electricity is passed embodying an anode or terminal of metallic tungsten and a cathode consisting of a tungsten spiral electrically heated". The action produces a chemical reaction in the glass that produces a faint violet color throughout the lens.
The Tillyer U.S. Pat. No. 1,644,798 shown another method of marking in which a stannous chloride solution is applied to the finished surface by a brush, rubber stamp or stencil. The treatment alters the surface tension of liquids on the lens so that condensation of moisture on a treated part has different size globules than on the untreated surfaces.
Still another method of marking glass lenses is shown in the Gallasch U.S. Pat. No. 1,607,395. Gallasch applied a waxy substance of balsam, bees wax or candelilla which is applied to the surface of the lens. The lens and material are then heated. The resultant mixture produces a chemical conversion on the surface of the glass that results in a visible marking when water condenses thereon.
The Tanaka U.S. Pat. No. 4,157,892 shows a method of coloring a water absorbent plastic by immersing the plastic in a diazonium double salt and then exposing the plastic to ultraviolet light in portions which are not to be colored.
Still another method of marking intraocular lens is shown in the Zdrok U.S. Pat. No. 4,039,827. Zdrok uses the technique of altering the refractive index of the lens by exposing the lens to ultraviolet radiation of sufficient intensity to create a slight differential in the refractive index of the lens in the region of the exposure.
Most of the above-indentified prior art patents use some method of marking glass lenses either on a permanent or temporary basis. The Zdrok patent, which is useable with plastic lenses, changes the inherent characteristics of the lens through the application of heat or radiation. In contrast, the present invention provides impregnation of the lens surface with a fluorescent material which, under normal conditions, is invisible; however, when ultraviolet light is shined on it the lens fluoresces.